Process for the separation of unreacted sugars from reaction mixtures obtained in the production of sugar fatty acid esters from sugars and fatty acid alkyl esters



United States Patent 2 Claims. (Cl. 260234) In-the production of sugar fatty acid esters, especially sugar monofatty acid esters, from sugars, such as e.g. saccharose, raffinose or trehalose, and fatty acid alkyl esters, such as e.g. stearic acid, oleic acid or palmitic acid methyl ester, in dimethyl formamide, dimethyl acetamide, dialkyl sulphoxide or butyrolactone, it is necessary to use an excess of sugars, referred to the amount of fatty acid alkyl esters employed, and, after termination of the reaction, to separate the unreacted sugars from the sugar fatty acid esters formed.

The present invention relates to a process for the separation of unreacted sugars from the reaction mixture obtained in such a production of sugar fatty acid esters; the process is characterised in that the reaction mixture which still contains the dimethyl formamide, dimethyl acetamide, dialkyl 'sulphoxide or butyrolactone, is mixed with those aliphatic hydrocarbons containing halogen or keto groups, or with those aromatic halogen-containing or halogen-free hydrocarbons which are miscible with dimethyl formamide, dimethyl acetamide, dialkyl sulphoxide or butyrolactone, and that the sugars which precipitate, are separated.

-Hydrocarbons suitable for carrying out the present invention are, for example, methylene chloride, chloroform, 1,2-dichloroethane, 1,2-dichloropropane, acetone, methyl ethyl ketone as well as benzene, toluene, xylene andchlorobenzene.

The necessary amounts of these hydrocarbons can easily be established by preliminary experiments. In general, it is recommended to use an amount of hydrocarbons at least equal to that of the solvents dimethyl formamide, dimethyl acetamide, dialkyl sulphoxide or butyrolactone, used for the production of the sugar esters.

The temperature of the reaction mixture to be mixed with the hydrocarbons according to the invention can lie between 20 and 90 C., but preferably between 40 and 60 C. If desired, the reaction mixture which still contains the dimethyl formamide, dimethyl acetamide, dialkyl sulphoxide or butyrolactone can also be added to the hydrocarbons. In order to complete the separation of the unreacted sugars, the mixture consisting of the reaction mixture and the hydrocarbons according to the invention is expediently thoroughly stirred for some time.

3,251,829 Patented May 17, 1966 By means of the process of the present invention it is possible to liberate the sugar fatty acid esters from the unreacted sugars in a simple way and without loss, so that they can subsequently be worked up in usual manner.

The unreacted sugars thereby precipitate in a form in which they can easily be filtered off; they can then directly be used again for the production of sugar esters. Due to this fact, the process of the invention is superior to the knOWn processes in which the solvent employed is first removed from the reaction mixture by evaporation and the unreacted sugars are then separated from the residue by selective dissolving by means of a dilute aqueous common salt solution or by means of a mixture of butanol and a dilute common salt solution. These methods involve considerable losses of sugar fatty acids, and the recovery of the unreacted sugars from the aqueous common salt solutions is very cumbersome.

Example 308 g. (0.9 mol) of saccharose, 89.4 g. (0.3 mol) of stearic acid methyl ester and 3 g. of potassium carbonate are reacted in known manner in 1.2 litres of dimethyl formamide to give the saccharose monofatty acid ester. When the reaction is completed, 2.2 litres of 1,2-dichloropropane are added with stirring within 45 minutes to the solution at C., the temperature is maintained at 60 C., and the reaction mixture subsequently further stirred at 60 C. for 10-15 minutes. The precipitated sugar is then filtered oif and dried in a vacuum. The 1,2-dichloropropane is distilled off from the filtrate at 40-50" C. and 15 mm. Hg, and the remaining solution of the sugar ester in dimethyl formamide is worked up in known manner.

We claim: 7

1. The process for the separation of unreacted sugars from the reaction mixture obtained during the production of sugar fatty acid esters by reacting fatty acid alkyl esters and excess amounts of a sugar in a reaction medium selected from the group consisting of dimethyl formamide, dimethyl acetamide, dialkyl sulphoxide and butyrolactone, said process consisting of the steps of mixing the reaction mixture containing said reaction medium with an agent selected from the groups consisting of halogenated aliphatic hydrocarbons, halogenated aromatic hydrocarbons, and halogen-free hydrocarbons which are miscible with said reaction medium to thereby precipitate said excess sugar and separating said precipitated sugar.

2. The process of claim 1 wherein said sugar is saccharose, said reaction medium is dimethyl formamide, and 1,2-dichloropropane is the mixed agent.

References Cited by the Examiner UNITED STATES PATENTS 2,893,990 7/1959 Hass et al 260234 2,931,802 4/1960 Tovey et a1. 260234 2,938,716 8/1960 Davis 260234 LEWIS GOTTS, Primary Examiner. 

1. THE PROCESS FOR THE SEPARATION OF UNREACTED SUGARS FROM THE REACTION MIXTURE OBTAINED DURING THE PRODUCTION OF SUGAR FATTY ACID ESTERS BY REACTING FATTY ACID ALKYL ESTERS AND EXCESS AMOUNTS OF A SUGAR IN A REACTION MEDIUM SELECTED FROM THE GROUP CONSISTING OF DIMETHYL FORMAMIDE, DIMETHYL ACETAMIDE, DIALKYL SULPHOXIDE AND BUTAYROLACTONE, SAID PROCESS CONSISTING OF THE STEPS OF MIXING THE REACTION MIXTURE CONTAINING SAID REACTION MEDIUM WITH AN AGENT SELECTED FROM THE GROUPS CONSISTING OF HALOGENATED ALIPHATIC HYDROCARBONS, HALOGENATED AROMATIC HYDROCARBONS, AND HALOGEN-FREE HYDROCARBONS WHICH ARE MISCIBLE WITH SAID REACTION MEDIUM TO THEREBY PRECIPITATE SAID EXCESS SUGAR AND SEPARATING SAID PRECIPITATED SUGAR. 